Alternative fuels are becoming increasingly more attractive for a number of reasons including reducing foreign oil dependence, environmental and emission concerns, and government mandates. Biodiesel is one alternative fuel that is gathering increasing attention because it may be made from a sustainable source. That is, biodiesel is commonly made by transesterifying an oil such as vegetable oil with, for example, methanol to obtain a fatty acid methyl ester also called FAME. Typically, biodiesels like FAME are blended with a petroleum-derived diesel, i.e., petrodiesel, in various amounts. For example, A B5 blend is typically 5% biodiesel by volume in petrodiesel, a B10 blend is typically 10% biodiesel by volume in petrodiesel, a B20 blend is typically 20% biodiesel, etc.
Unfortunately, blending FAME with petrodiesel often increases the cloud point, i.e., the temperature at which a cloud of crystals first appears under standard cooling conditions. The amount of the cloud point increase usually goes up as the volume of FAME goes up. This is problematic in that there are often rigorous cloud point specifications in order that the fuel functions properly in the engine even in cold weather.
It has been suggested that FAME could be eliminated and fatty acid isopropyl esters (FAIE) substituted for FAME in a petrodiesel blend. For example, Wang suggests that “for better cold weather performance, isopropyl esters look very promising as a neat blend.” See, P. Wang, “The production of isopropyl esters and their effects on a diesel engine,” M. S. Thesis, Iowa State University, 2003 at p. 4. See also, W. H. Wu, T. A. Foglia, W. N. Manner, R. O. Dunn, C. E. Goering, and T. E. Briggs, JAOCS, 75, 1173 (1998); I. Lee, L. A. Johnson, and E. G. Hammond, ibid., 72, 1155 (1995); and P. Wang, M. Tat, and J. Van Gerpen, ibid., 82, 845 (2005). Unfortunately, FAIE is generally more costly to produce than FAME due to, for example, the cost of isopropanol. Therefore, there is a high cost to eliminate FAME—especially when it can be as much as from about 5 to about 20% by volume of the biodiesel:petrodiesel blend.
Accordingly, what is needed are cost-effective biodiesel compositions that will not negatively affect cloud point properties over a range of various petrodiesel blend compositions. Advantageously, the instant invention offers cost-effective biodiesel compositions which yield improved cloud point properties when blended over a range of various petrodiesel blend compositions.
In one embodiment the invention pertains to a biodiesel composition comprising at least about 50 percent by volume fatty acid methyl ester. The biodiesel composition also comprises an amount of fatty acid branched C3-C4 alkyl ester sufficient to reduce the cloud point of a 10:90 liquid volume composition of a biodiesel:petrodiesel blend to at least ⅔ of the total cloud point reduction as measured in degrees Celsius of a 10:90 liquid volume composition of a fatty acid branched C3-C4 alkyl ester:petrodiesel blend.
In another embodiment the invention pertains to a composition comprising petrodiesel and from about 4 to about 22 volume percent biodiesel based on the total volume of the composition. The biodiesel comprises fatty acid branched C3-C4 alkyl ester and fatty acid methyl ester. The fatty acid branched C3-C4 alkyl ester comprises from about 10 to about 50 volume percent of the biodiesel based on the total volume of biodiesel.
In another embodiment the invention pertains to a composition comprising bodiesel and petrodiesel. The petrodiesel comprises at least about 78% by volume based on the total volume of the composition. The biodiesel comprises fatty acid methyl ester and from about 5 to about 50 volume percent of fatty acid isopropyl ester based on the total volume of the biodiesel.